Drought management - a growing need

Thai Pongal, which was celebrated in Sri Lanka last weekend, is the Tamil Hindu festival of good luck and bounteous harvests. People give thanks to the Lord Shiva, to Surya, the sun god and Bhogi, the rain god (Indra).

According to folklore, if it does not rain on Thai Pongal day, there will be no rain for days to come. It certainly didn’t rain last weekend, so are we about to go into a drought? The possibility is there: January, February and March are the months of least rainfall, islandwide. However, in the Dry and Arid Zones it is equally dry in June-August, and it is in this period that droughts tend to occur.

Drought can also occur in times of normal rainfall, when the usage of water in wells, reservoirs and aquifers exceeds replenishment rates and the reserves fall below a sustainable level, or when there is insufficient water to support agricultural production.

Sri Lanka has no standardised definition of drought. The Department of Meteorology defines dry periods as follows:

• Absolute drought - rainfall of 0.01 inch (0.25 mm) or more is not recorded on any day during a period of at least 15 consecutive days.
• Partial drought - the mean daily precipitation does not exceed 0.01 inch (0.25 mm) for a period of at least 29 consecutive days.
• Dry Spell - Any period of at least 15 consecutive days to none of which is credited with 0.04 inch (1.0 mm) of rain or more.

Drought mitigation plan

Other authorities have variant characterisations, for example, a prolonged deficiency of rainfall; when reservoirs are depleted and the crops are threatened by a lack of water; if rainfall is less than four inches within a period of three months; or if any region of the country receives less than 75 percent of its normal rainfall during the Maha or Yala seasons.

Given that we have no standard for identifying a drought, it should come as no surprise that we likewise have no national or regional drought mitigation plan. The necessity for such a scheme is nevertheless dire.

The 2004 Boxing Day Tsunami affected fewer than a million people; although, admittedly, it killed over 35,000 of them. The Sri Lanka Disaster Management Centre has plans on how to cope with another.

However, a drought can affect up to one and a half million people in a single year, as in the great drought of 2001, in which 80 percent of the people of Hambantota district were adversely impacted. Furthermore, large-scale droughts occur every three-four years.

Over the past four decades more than 12.5 million people have been affected. Over 11,000 hectares of paddy land are destroyed each year due to lack of water.

Weather pattern

The climatic changes that are occurring, as global warming gets into its stride, are likely to cause greater swings in the weather pattern. Combined with the loss of forest cover in the watersheds, they can cause greater extremes of flooding and drought.

Droughts occurred in antiquity as well. It was in order to counter the periodic shortages of water that our forebears constructed one of the greatest hydraulic civilisations in history, based on an intricately inter-woven system of rivers, canals, weirs and tanks.

Apart from the many large reservoirs (for which the word ‘tank’ is so inadequate) built by the ancient kings, there were thousands of village tanks, which generally followed a cascade pattern within a catchment area. The upkeep of these tanks was undertaken by the villagers themselves. Villages were centred on the tank, with dwellings lying at either end of the bund; village self-governance evolved around the need for irrigation management.

In spite of this, disaster-level droughts did occur. Unfortunately our ancestors lacked all the resources now available to us, especially the technological ones. It behoves us to use those resources wisely as befits the memory of our ancestors.

It should be borne in mind that the ancients didn’t have electricity, and hence did not depend on using part of their water for hydro-electric generation. We do, and mini-hydro suffers even more from drought than do major hydro-electric schemes.

Renewable energy

Electricity shortages due to drought could be avoided somewhat by the addition of renewable energy, particularly solar electricity and wind power. Solar in particular can be used efficiently in the daytime, with hydro-electricity as a back-up and for use at night.

In part, we could avoid the fullest effects of drought by reviving the hydraulic works of the ancients. There are over 15,000 ancient small tanks, of which only half are operational. The rehabilitation of the remainder could mitigate the effects of average droughts.

For severe droughts, we would need a mitigation plan. This presupposes the existence of a national drought risk map, forecasting and early warning systems and monitoring systems. It would be the data from these that would enable an effective response plan.

The response would be in the form of giving early warning and later providing essential water, foodstuffs, and financial aid where needed.

In addition, a long-term programme to banish drought needs to be put in place. This would mean using the excessive rainfall in times of flood during droughts. Half of Ratnapura District, for example is subject to heavy rainfall and flooding, whereas the other half suffers from periodic drought. The solution is obviously to balance the two out.

The process is helped by the fact that both drought and flood prevention require many of the same measures. Better watershed management and re-planting water-retaining forests help keep all the water from discharging at once, leaving more available for use in dry periods.

It has also been suggested that the excess waters of rivers such as the Kelani, Kalu, Bentota and Gin could be diverted during time of flood, to storage reservoirs upstream from high drought-risk areas. Whatever long-term solutions are to be adopted, planning should begin as soon as possible.